1. Field of the Invention
The present invention relates to a method of and an apparatus for cleaning a substrate, and more particularly to a method of and an apparatus for cleaning a semiconductor wafer or the like to remove an unwanted interconnection material such as copper (Cu) or the like that has been attached to a periphery and a reverse side of the substrate upon growth of a film on the substrate.
2. Description of the Related Art
More attempts are being made to use copper, which has a low electric resistivity and is highly resistant to electromigration, as a metal material for forming interconnections on a semiconductor substrate, rather than aluminum and aluminum alloys. Copper interconnections are generally formed by embedding copper in minute recesses defined in a surface of the semiconductor substrate. CVD, sputtering, and plating processes are used to form copper interconnections. According to any of these processes, a copper film is deposited on the entire surface of the semiconductor substrate, including its periphery, or on the surface of the semiconductor substrate while sealing its periphery, and thereafter unwanted deposited copper is removed from the semiconductor substrate by chemical mechanical polishing (CMP). In this copper film growth process, when the sealing is incomplete, the copper film is deposited on a periphery, i.e. edge of the substrate, and a sputtered film of copper is attached to a reverse side of the substrate.
On the other hand, copper can easily be diffused into a silicon oxide film during a semiconductor fabrication process, thereby impairing electric insulation of the silicon oxide film. Thus, the remaining unnecessary copper needs to be completely removed from the substrate. Furthermore, the copper deposited upon film growth on the periphery (edge and beveled surface) of the substrate other than a circuit area is not only unnecessary, but may cause cross contamination in subsequent processes of delivering, storing, and processing the substrate. For these reasons, it is necessary that the remaining deposited copper on the periphery of the substrate be completely removed immediately after the copper film growing process or the CMP process.
Various efforts have been proposed to remove unwanted copper deposits from semiconductor substrates. According to one attempt, while a substrate with a protective coating on a surface of a copper film on an upper circuit region is being rotated in a horizontal plane, a periphery of the substrate is supplied with a copper etching solution to dissolve and remove copper attached to the periphery of the substrate. Another proposed effort is concerned with a process of immersing a substrate with a protective coating in an acid solution to etch away a metal film formed on a periphery of the substrate.
However, while conventional copper removal processes are capable of removing unwanted copper deposits from the periphery of substrates, they cannot remove a natural oxide film formed on a surface of copper on a circuit, which needs to be removed separately, and they fail to remove copper deposits from a reverse side of the substrate simultaneously with the removal of copper deposits from the surface on which the circuit is formed. Copper deposits are removed from a periphery of the substrate over different widths (edge cutting widths) depending on the purpose for which the substrate will be used. Since the conventional copper removal processes fail to set the edge cutting width to freely selected values, they cannot handle a wide variety of types of substrates. This problem holds true for other interconnection materials including tungsten, ruthenium, various silicides, and additional materials other than copper and electrode materials.
It is therefore an object of the present invention to provide a method of and an apparatus for cleaning a substrate to reliably remove an interconnection material such as copper from a periphery and a reverse side of the substrate while removing a natural oxide film formed on a surface of copper on a circuit of the substrate, and allowing an edge cutting width to be set to a freely selected value.
According to the present invention, there is provided a method of cleaning a substrate, comprising: supplying an acid solution to a central portion of a surface of a substrate while rotating the substrate; and supplying an oxidizing agent solution to a periphery of the substrate.
Any natural oxide film of copper, for example, formed on a circuit area on the surface of the substrate is removed, and hence prevented from growing, by the acid solution which is supplied to the central portion of the surface of the substrate and spreads over the entire surface of the substrate. A copper film, for example, attached to the periphery of the substrate is oxidized by the oxidizing agent solution, and etched away and dissolved by the acid solution.
The method further comprises supplying an oxidizing agent solution and an acid solution to a reverse side of the substrate. Copper, for example, attached to the reverse side of the substrate, together with silicon of the substrate, is oxidized by the oxidizing agent solution and etched away by the acid solution. The copper is removed from the reverse side of the substrate simultaneously with the removal of the film of copper from the surface of the substrate.
The oxidizing agent solution and the acid solution may be supplied from respective different nozzles to the reverse side of the substrate. If the supply of the oxidizing agent solution is stopped first, then a hydrophobic surface is produced on the reverse side of the substrate. If the supply of the acid solution is stopped first, then a hydrophilic surface is produced on the reverse side of the substrate. Therefore, the reverse side of the substrate can be adjusted to meet a subsequent process requirement.
The acid solution comprises at least one of hydrochloric acid, hydrofluoric acid, sulfuric acid, citric acid, and oxalic acid.
The oxidizing agent solution comprises at least one of ozone, hydrogen peroxide, nitric acid, and hypochlorous acid.
According to the present invention, there is also provided an apparatus for cleaning a substrate, comprising: a substrate holder for holding and rotating a substrate; a central nozzle disposed above a central portion of a surface of the substrate which is held by the substrate holder; and an edge nozzle disposed above the substrate which is held by the substrate holder. The edge nozzle is movable from a periphery of the substrate toward the central portion thereof and/or vertically with respect to the surface of the substrate. For supplying the acid solution from the central nozzle and the oxidizing agent solution from the edge nozzle to etch a periphery of the substrate, the position and/or height of the edge nozzle can be varied to set an edge cutting width freely.
The edge nozzle is adjustable to vary an angle between solution ejected from the edge nozzle and the surface of the substrate.
The edge nozzle is adjustable to vary an angle between an extension line, of a line defined as projection of the solution ejected from the edge nozzle onto the surface of the substrate, and a line tangent to an outer circumference of the substrate at an intersection point with the extension line.
The orientation of the edge nozzle with respect to the surface of the substrate can be selected as desired to change the direction in which the solution ejected from the edge nozzle is applied to the surface of the substrate, for thereby preventing the solution from being scattered around and thus achieving a good etching configuration.
According to the present invention, there is provided a method of cleaning a substrate having a circuit on which copper is deposited, comprising: supplying an acid solution to a central portion of a surface of the substrate and spreading the acid solution over the entire surface of the substrate while rotating the substrate; and dissolving away oxidized copper on upper and outer peripheral surfaces of a periphery of the substrate.
The acid solution comprises non-oxidizing acid. The non-oxidizing acid comprises at least one of hydrochloric acid, hydrofluoric acid, sulfuric acid, citric acid, and oxalic acid.
The oxidizing agent solution comprises at least one of ozone, hydrogen peroxide, nitric acid, and hypochlorous acid.
The method further comprises supplying an oxidizing agent solution to a reverse side of the substrate that is opposite to the surface of the substrate.
According to the present invention, there is provided an apparatus for cleaning a substrate having a circuit on which copper is deposited, comprising: a substrate holder for holding and rotating a substrate; a central nozzle for supplying an acid solution to a central portion of a surface of the substrate which is held by the substrate holder; and an edge nozzle for supplying an oxidizing agent solution to a periphery of the substrate.
According to the present invention, there is provided a plating apparatus for plating a surface of a substrate with metal in a housing unit. The plating apparatus comprises: a cassette stage for placing a substrate cassette thereon; a plating unit for plating the surface of the substrate; and a first cleaning apparatus for cleaning the plated substrate at least by an acid solution. The first cleaning apparatus comprises a substrate holder for holding and rotating the substrate, a central nozzle for supplying an acid solution to a central position of the surface of the substrate held by the substrate holder, and an edge nozzle for supplying an oxidizing agent solution to a periphery of the surface of the substrate. The plating apparatus further comprises: a second cleaning apparatus for cleaning the plated substrate with pure water; and a transfer device for transferring the substrate.